This invention relates generally to gas turbine engines and more particularly to gas turbine engine components formed in part from high temperature foil materials.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. In a turbofan engine, which typically includes a fan placed at the front of the core engine, a high pressure turbine powers the compressor of the core engine. A low pressure turbine is disposed downstream from the high pressure turbine for powering the fan. Each turbine stage commonly includes a stationary turbine nozzle followed in turn by a turbine rotor.
Gas turbine engine hot section components, in particular the high pressure turbine section components, operate at extremely high temperatures and need to be cooled to have acceptable longevity. Cooling is typically provided by extracting relatively cool air from an upstream location of the engine and routing the cooling air to components where it is needed. Conventionally the components to be cooled are hollow and have provisions for receiving and distributing the cooling air by various methods, for example the components may be film cooled by providing a plurality of passages which eject a blanket of cooling air over the surface of the component, or the components may be convectively cooled by causing the cooling air to flow through various internal passages.
Known cooling arrangements often include a plurality of openings in the trailing edge of an airfoil through which cooling air is discharged. These openings may take the form of a pressure side bleed slot arrangement, in which the airfoil pressure side wall stops short of the extreme trailing edge of the airfoil, creating an opening which is divided into individual bleed slots by a plurality of longitudinally extending lands incorporated into the airfoil casting. These slots perform the function of channeling a thin film of cooling air over the surface of the airfoil trailing edge. Airfoils having such a pressure side bleed slot arrangement are known to be particularly useful for incorporating a thin trailing edge. In effect, the trailing edge thickness of the airfoil is equal to that of the suction side thickness alone. This is desirable in terms of aerodynamic efficiency. Ideally, the slot exits are extended toward the trailing edge as far as possible to maintain a good film cooling effectiveness. However, because of casting process limitations on minimum metal thickness, the slots have exits at a finite distance upstream from the trailing edge. This results in an area of uncovered film cooling downstream of the slot exits, which can allow mixing of hot flowpath gasses with the cooling air flow and often results in severe oxidation.
Accordingly, there is a need for gas turbine engine airfoils having improved trailing edge cooling effectiveness.
The above-mentioned need is met by the present invention, which provides a turbine airfoil having a plurality of pressure side bleed slots through which cooling air is discharged. A portion of the slot openings are covered with an outer wall which comprises a high temperature foil.